As known to those skilled in the art, LED modules used for illumination purposes, including general indoor as well as outdoor illumination, generally have a support structure, for example a circuit board with associated heat sink and mounting materials on which several LED components may be positioned, to include the chips, dies and optics, both primary and secondary, of the LED assembly. In order to protect the LED components from ambient environmental conditions in outdoor applications, the LED components are typically covered with optically transparent elements, which elements may also comprise the optics of the LED module.
It is desirable to ensure that the elements covering the LEDs are not adversely affected in their optical properties by either the high heat that results from LED operation or by other external influences, and of particular concern is the avoidance of any fogging or distortion of any and all materials positioned within the light path emanating from the LEDs in order to permit maximum light output and distribution to occur. It is known, however, that harmful gases can form in the LED modules during operation caused, for example, by the manufacturing flux residues or other resins used in or on the manufacture of the LED assembly, which may in turn lead to the fogging of plastics enclosing the LEDs, for example lenses and optics, especially those made of silicone materials. This effect is attributed, for example, to the cleavage of diphenyl groups. Also, and as known, the fogging of the lens/optics, and or other cover elements, can occur either due to thermal or photochemical reactions.
Accordingly, there is a need for an LED module adapted for use in outdoor applications which does not exhibit this fogging phenomena, even after periods of prolonged LED operation.